Bill Sharkey, the underdog in Saturday's heavyweight fight at the Miami Beach Convention Center, has spent this week as a supporting actor to Kallie Knoetze, the second-ranked heavyweight contender.

Knoetze (16-2) continued to carry the show today. After weighing in at 217 pounds to his rival's 198, he assured newsmen he would take care of Sharkey (18-2-1) without much difficulty.

Sharkey's face bears the scars of 21 professional fights and countless street fights in his native New York City. But the worst scars Sharkey bears are inside. Nearly 10 years ago he killed a man in a street fight. Sharkey, now 29, spent nearly five years in prison.

Knoetze's street behavior has become the major issue of this fight. Because he shot a black teen-ager in the leg while working as a policeman in South Africa, civil rights activists have unsuccessfully tried to stop the fight (WDVM-TV-9, 4:30 p.m.)

The State Department acknowledged today that it cannot stop the heavyweight bout.

But the government is asking U.S. District Judge Norman Roettger, based in Florida, to call a hearing concerning Knoetze's U.S. work permit, which Secretary of State Cyrus Vance had revoked Tuesday.

The move to bar Knoetze from fighting in the United States -- even if sustained in court -- would be too late to stop the fight.

Despite the controversy, Knoetze has seemed cheerful and confident.

"He's a good fighter -- that's why he's fighting me," Knoetze said. "We both have two hands, but I've got too much for him."

Knoetze, asked whether he expects to knock out Sharkey, said, "Definitely."

When the gates open for the 12-bout program, there will be a demonstration by activists protesting Knoetze's appearance.

Knoetze has tried to avoid the issue of his alleged violence in South Africa. Sharkey does not try to avoid the issue of his violence. He says a prison psychiatrist was first to make him understand it.

"I didn't realize until after I had committed my most serious crimes that I had a very aggressive personality," Sharkey said. "A psychiatrist pointed this out to me and showed me how to overcome it.

"He told me, 'Instead of always filling up the glass and letting it overflow, just learn to tip the glass.'"

"Boxing is the perfect outlet for me," Sharkey said.

Boxing became Sharkey's outlet because of Clem Florio, an uncle who is an ex-fighter and the horse racing handicapper of The Washington Post.

Florio's efforts began when Sharkey was jailed in 1970.

"When they first threw me in jail, my uncle talked to me in there and convinced me I was going nowhere fast," Sharkey said. "We stayed close and I decided while I was in there that I'd fight.

"I knew I could fight because (as an amateur) I'd see the way guys' eyes would roll up when I hit them.Plus, I never lost a street fight in my life."

Sharkey was a big loser in his most decisive street victory. His opponent was dead.

"It wasn't anything premediated," Sharkey said, reluctant to discuss details of the brawl. "It was a street fight. Things happen so fast and you have to deal with it so fast.

"But even then, I was too smart for that."

Florio says Sharkey has started to blossom. Saturday he will meet a formidable puncher with a weight edge that was announced as 19 pounds.

"I'm really 196," Sharkey said. "That was only to make me bigger, instead of like a midget. I'm proud of it, of course. I'm smaller than they are and I still kick their tail."